A Professor Wants to Examine the Effects of Diet on Learning.He

A professor wants to examine the effects of diet on learning.He places some laboratory rats on a starvation diet (Group A) but eliminates only desserts from the diet of a second group (Group B) .During the experiment,the professor discovers that he needs more Group B rats,so he catches some in a local alley.The results of the experiment show that Group B rats are faster at learning a maze,so the professor concludes that diet is related to learning speed.Which statement about his conclusion is most accurate?

A) The professor's conclusion is correct because the number of rats in each group are the same.
B) The professor's conclusion is correct because the two groups of rats were on a different diet.
C) The professor's conclusion is incorrect because the type of rat was a confound.
D) The professor's conclusion is incorrect because the study is correlational.